Known in the art are dam spillways made in the form of open or closed channels communicating the reservoirs upstream and downstream of the dam and provided with the water flow kinetic energy dissipators (cf. Specification to U.S. Pat. No. 2,103,600 cl. 61-18, filed Dec. 21, 1935, Specification to USSR Inventor's Certificate No. 124, 370 cl. E02B 8/06, filed Feb. 10, 1959 and Specification to USSR Inventor's Certificate No. 697,628 cl. E02B 8/06, filed Oct. 3, 1974). Owing to the use of kinetic energy dissipators, such spillways are capable of discharging not only the principal function consisting in purposeful passage of the required water flow from the forebay into the afterbay, but also in preventing gradual destruction of the spillway walls and the afterbay bottom caused by the water flow. Spillways with kinetic energy dissipators are ordinarily installed on diversion dams erected in running-water reservoirs and intended for a comparatively small increase in the water level in the reservoir upstream of the dam with the purpose of, e.g., ensuring safety of navigation. The difference in the forebay and afterbay levels on such a dam being relatively small, its use, e.g. for power generation, is impracticable from the point of view of economy. On the other hand, said difference is detrimental as regards water passage from the forebay into the afterbay, for the high velocity water head arising due to said difference brings about gradual destruction of the spillway walls located in the vicinity of the afterbay and the bottom thereof. To prevent destruction, the prior art designs employ dissipation of the kinetic energy of the water flow being passed. To this end, the outlet sections of the spillway are provided with kinetic energy dissipators made either in the form of small bluff baffle piers causing considerable energy losses when flown around (cf. U.S. Pat. No. 2,103,600) or in the form of a screen dividing the flow into separate jets whose confluence results in dissipation of the flow kinetic energy (cf. USSR Inventor's Certificate No. 124,300), or in the form of widening troughs installed step-wise on narrowing buttresses (cf. USSR Inventor's Certificate No. 697,628) wherein energy dissipation is effected due to both factors employed in the first two solutions.
However, in the prior art spillways the energy of the high velocity water flow is completely wasted to be lost irreversibly.
Also known are devices (cf. Specifications to U.S. Pat. Nos. 3,461,674 cl. 61-2, filed Jan. 20, 1967 and 3,893,924 cl. 210-220, filed Oct. 19, 1973) intended for aeration of water in reservoirs and made in the form of a system of pipes with perforations, laid in the proximity of the reservoir bottom, through which perforations air preliminarily mixed with water issues into the bottom layers of the reservoir. Air-water mixture under a pressure exceeding that in the reservoir bottom layers is supplied into said pipes either with the aid of a mixer (cf. U.S. Pat. No. 3,461,674) whereto air and water are delivered by a fan and a pump respectively or by means of an air-water ejector (cf. U.S. Pat. No. 3,893,924) whereto air is carried by the water injected by the pump. However, air supply calls for certain consumption of power to drive the pump and the fan, this consumption for a definite period of time, e.g. a year, becoming quite appreciable due to constant operation of said devices. Moreover, these solutions do not feature design characteristics which would allow them to be used as dam spillways.
Another prior art dam spillway to pass water from a forebay into an afterbay over the dam crest includes a vertically disposed mixing chamber having an inlet section opening into the atmosphere and communicating with a horizontally arranged diffuser (cf. Specification to USSR Inventor's Certificate No. 340,735 cl. E02B 7/00, filed Jan. 4, 1971). The downward flow of water being passed through said spillway may entrain air into the mixing chamber via the mixing chamber inlet section opening into the atmosphere. In said chamber a certain portion of the kinetic energy of the water is imparted to the air. Owing to such utilization of the water kinetic energy generated as a result of the transformation of the difference in the forebay and afterbay levels, said prior art device may ensure, simultaneously with passing water over the dam, aeration of the water, thereby contributing to saturation of the latter with oxygen.
However, the water in said prior art device flows down into the mixing chamber in a single stream, owing to which circumstance the air-water interface is comparatively small. Accordingly, the amount of air entrained by the water flow and, consequently, the degree of the water saturation with oxygen are also small. The low air flow rate in said prior art device results in a low efficiency of dissipating the water kinetic energy by admixing air to the water.